The invention relates to methods and apparatus for removal of transvenous endocardial leads from a patient's heart and the venous path thereto.
In the past, various types of endocardial leads and electrodes thereof have been introduced into different chambers of a patient's heart including the right ventrical, right atrial appendage, and atrium as well as the coronary sinus. These flexible leads usually are composed of an insulator sleeve that contains an implanted helical coil conductor that is attached to an electrode tip. This electrode is placed in contact with myocardial tissue by passage through a venous access, often the subclaven vein or one of its tributories, which leads to the endocardial surface of the heart chambers. The tip with the electrode contact is held in place by trabeculations of myocardial tissue. The tips of many available leads include flexible tines, wedges, or finger-like projections which extend radially outward and usually are molded from and/are integral with the insulating sheath of the lead. These tines or protrusions allow surrounding growth of tissue and scar in chronically implanted leads to fix the electrode tip in position in the heart and prevent dislodgement of the tip during the life of the lead. In "acute placement" of the electrode or tip a blood clot forms about the flanges or tines (due to enzymes released as a result of irritation of the trabeculations of myocardial tissue by the presence of the electrode tip) until scar tissue eventually forms, usually in three to six months. The tines or wedges or finger-like projections allow better containment by the myocardial trabeculations of muscle tissue and prevent early dislodgement of the lead tip. Other types of "screw-in" tips include the electrodes described in U.S. Pat. Nos. 4,209,019 and 3,974,834, assigned to Medtronic, Inc. Although the state of the art in implemented pulse generator or pacemaker technology and endocardial lead technology has advanced considerably, endocardial leads nevertheless occasionally fail, due to a variety of reasons, including breakage of a lead, insulation breaks, breakage of the inner helical coil conductor thereof and increase in electrode resistance. Also, in some instances, it may be desirable to electronically stimulate different portions of the heart than are presently being stimulated with leads already in place. There are a considerable number of patients who have one or more, and sometimes as many as four or five unused leads in their veins and heart.
Although it obviously would be desirable to be able to easily remove such unused leads, in the past surgeons usually have avoided attempts to remove inoperative leads because the risk of removing them exceeded the risk of leaving them in. The risks of leaving unused myocardial leads in the heart and venous path include increased likelihood that an old lead may be the site of infection which may necessitate removal of the lead to prevent continued bacteremia and abcess formation which, in turn, may lead to fatal complications. Furthermore, there is an increased likelihood of the formation of blood clots in the atrial chamber about entangled leads. Such clots may embolize to the lung and produce severe complications and even fatality. Furthermore, the presence of unused leads in the venous pathway and inside the heart can cause considerable difficulty in the positioning and attachment of new endocardial leads in the heart.
Thus, it is clear that the potential for infection and other complications increases rapidly as a number of old or unused endocardial leads in the heart and venous pathway increases.
Removal of an inoperative lead sometimes can be accomplished by applying traction and rotation to the outer free end of the lead but only if done prior to fixation of the lead tip in the trabeculations of myocardial tissue by scar formation or large clot development. Even then, it is possible that a clot has formed so the removal of the leads causes various sized emboli to pass to the lungs, producing severe complications.
In cases where the lead tip has become attached by scar tissue to the myocardial wall, removal of the lead always has presented major problems and risks. Porous lead tips that are sometimes used may have ingrowth of scar tissue attaching them to the myocardial wall. Sufficient traction on such leads in a removal attempt could cause disruption of the myocardial wall prior to release of the embedded lead tip, causing fatality. The tines or flanges of other types of leads that are not tightly scarred to the myocardial wall present similar risks. Even if screw-in tip electrodes of the kind mentioned in the Medtronic patents referred to above are used, wherein the tips theoretically can be unscrewed from the myocardial wall, unscrewing of such tips may be prevented by a channel of scar tissue and endothelium that surrounds the outer surface of the lead along the venous pathway. Such "channel scar" tissue prevents withdrawal because of tight encasement of the lead. Continual strong pulling or twisting of the outer free end of the lead could cause rupturing of the right atrial wall or right ventricular wall if there is such tight circumferential encasement of adherent channel scar tissue in the venous path. Such tight encasement by scar tissue in the venous pathway and in the trabeculations of the myocardial wall typically occurs within six months to a year of the initial placement of the lead.
The risks of removal of a lead by such traction and rotation of the lead are so high that if it becomes imperative that the lead be removed (as in the case of infection) most surgeons have elected to open the patient's chest and surgically remove the lead rather than attempt removal by applying traction and rotation thereto.
Clearly, there is a need for an improved method and apparatus for extracting "chronically placed" endocardial leads with minimal risk to the patient.
Accordingly, it is an object of the invention to provide an improved method and apparatus for extraction of endocardial leads with minimal risk to the patient.
It is another object of the invention to allow placement of new endocardial leads and electrodes without interference by old leads in the venous path or heart with the new leads.
It is another object of the invention to provide a method and apparatus for removal of infected leads without the need for open chest surgery.
Further experiments have been conducted on dogs with implanted leads, using the apparatus and method described in the above-identified parent application. In those experiments, two or more leads were implanted in the same vein leading to the dog's heart, and scar tissue had built up in the veins and around the leads. Calcified as deposits also were found, causing considerable difficulty in advancing the lead extracting structure through such scar tissue and/or deposits. Rotation of the dilating catheter to dilate and/or separate the scar tissue has resulted in undesired rotating of the vein, which can cause entanglement of the lead to be extracted with other leads to be removed, causing complications such as preventing passage of the lead extracting assembly into the heart cavities. Furthermore, rotation of the vein could cause rupturing of the vein, or rupturing of side veins that are attached thereto, and could also cause breaking of an operative endocardial lead in the same vein, or breaking of its insulation.
Therefore, it is a further object of the invention to provide a method and apparatus for separating scar tissue and/or other obstructions in a venous path to enable easy and safe advancement of the endocardial lead extraction apparatus described in the parent application through the venous path to the heart.